The present invention generally relates to surfactant compositions and methods for making and using such compositions. More particularly, the invention relates to compositions containing post-added xcex1-sulfofatty acid esters with detergent components, and methods for making and using the same.
Soaps made from animal fats have been used for many years to clean dishes, utensils and other materials. More recently, cleaning compositions have been formulated using other surfactants to enhance their cleaning performance. Typical surfactants include anionics, nonionics, zwitterionics, ampholytics, cationics and those described in. Surface Active Agents, Volumes I and II by Schwartz, Perry and Berch (New York, Interscience Publishers), in Nonionic Surfactants, ed. by M. J. Schick (New York, M. Dekker, 1967), and in McCutcheon""s Emulsifiers and Detergents (1989 Annual, M. C. Publishing Co.), the disclosures of which are incorporated herein by reference.
Anionic surfactants are a preferred surfactant for many cleaning applications due to the improved surface agent properties of these surfactants. A variety of anionic surfactants have been developed for cleaning applications. Linear alkyl sulfonates (xe2x80x9cLASxe2x80x9d) and alkybenzene sulfonates (xe2x80x9cABSxe2x80x9d) are two popular anionic surfactants. These surfactants are used alone or in combination with soaps (i.e., fatty acids), depending on the desired properties of the final composition. The use of ABS as surfactants has recently fallen into disfavor, however, due to their lesser biodegradability. The use of ABS and LAS surfactants is also disfavored for hard water applications, where the detergency of these surfactants decreases.
Recently, interest in xcex1-sulfofatty acid esters (also referred to hereafter as xe2x80x9csulfofatty acidsxe2x80x9d) has increased due to the superior cleaning properties of these surfactants in hard water. For example, methyl ester sulfonates (xe2x80x9cMESxe2x80x9d) retain higher detergency values than LAS or ABS as water hardness increases. Such improved hard water cleaning performance is beneficial because it allows this surfactant to be used in a wider variety of cleaning applications. This hard water xe2x80x9ctolerancexe2x80x9d is also beneficial because hard water is used in many areas of the world for cleaning.
The use of xcex1-sulfofatty acid esters has not been widely accepted, however, due to several disadvantages of such sulfofatty acids. xcex1-Sulfofatty acid esters are typically manufactured as salts. xcex1-Sulfofatty acid ester salts are typically a mixture of salt forms (e.g., mono- and di-salts). For example, MES has both mono- and di-salt forms (i.e., mono-sodium MES and di-sodium MES). While mono-salts of xcex1-sulfofatty acid esters have the desired surface active agent properties, di-salts have several undesirable properties that degrade the performance of the resulting composition. For example, the Kraft point of a C16 methyl ester sulfonate (xe2x80x9cMESxe2x80x9d) di-salt is 65xc2x0 C., as compared to 17xc2x0 C. for the mono-salt form of C16 MES. (The Kraft point is the temperature at which the solubility of an ionic surfactant becomes equal to its critical micelle concentration; below the Kraft point, surfactants form precipitates instead of micelles.): Higher proportions of di-salt cause more precipitation. The presence of large amounts of di-salts in xcex1-sulfofatty acid ester, therefore, results in a poorer quality xcex1-sulfofatty acid ester product, characterized by degraded performance and reduced application flexibility.
A related problem is that di-salts result from hydrolysis of xcex1-sulfofatty acid ester during storage and in detergent formulations. In particular, mono-salts of xcex1-sulfofatty acid ester hydrolyze in the presence of moisture and alkali-containing detergent components to form di-salts. For example, mono-sodium MES reacts with caustic soda (NaOH) in the presence of moisture to form a di-salt by the following reaction: 
In formulations where mono-sodium MES is well mixed with high pH components under aqueous conditions, the MES will hydrolyze nearly completely to the di-salt form. High pH components include builders, such as silicates or carbonates, and bases, such as sodium, hydroxide (NaOH). This chemical instability discourages the use of xcex1-sulfofatty acid esters in many cleaning applications.
Thus, there exists a need for cleaning compositions containing xcex1-sulfofatty acid ester that exhibit reduced di-salt formation by the, sulfofatty acid and hard water tolerance. The present invention surprisingly satisfies this need and more.
The present invention includes compositions comprising xcex1-sulfofatty acid ester that is post-added to other detergent components. The compositions comprise at least two portions. The first portion contains xcex1-sulfofatty acid ester. In one embodiment, the xcex1-sulfofatty acid portion consists of xcex1-sulfofatty acid ester and its manufacturing byproducts. In another embodiment, the xcex1-sulfofatty acid portion comprises other detergent components. In another embodiment, the xcex1-sulfofatty acid ester portion is free of additional detergent components that cause more than a minor amount of additional di-salt formation.
The second portion comprises other detergent components, according to the desired properties of the final composition. For example, such components can include, but are not limited to, secondary anionic surfactants, nonionic surfactants, cationic surfactants, zwitterionic surfactants, polymer dispersants, oxidizing agents, biocidal agents, foam regulators, foam stabilizers, binders, anticaking agents, activators, builders, hydrotropes, catalysts, thickeners, stabilizers, UV protectors, fragrances, soil suspending agents, polymeric soil release agents, fillers, brighteners, enzymes, salts, inert ingredients, and the like. In a preferred embodiment, the second portion includes detergent components that cause more than a minor amount of additional di-salt formation.
The first portion is prepared by providing the xcex1-sulfofatty acid ester, optionally combining the xcex1-sulfofatty acid ester with any other detergent components, as desired, and then forming the first portion. The second portion is formed by combining other detergent components and then forming them into the second portion. The first portion is post-added to the second portion by admixing the first portion with the second portion. Because the second portion is typically formed by processes, or includes detergent components, that cause additional di-salt formation, the amount of additional di-salt formation is reduced by post-adding the first portion to the second portion after such di-salt forming processes are completed, or partially segregating the xcex1-sulfofatty acid ester from such di-salt forming components.
Each portion typically comprises a plurality of particles, such as a powder, or beads, pellets, granules, and the like. When the portions are admixed, the particles are co-mingled, but remain physically distinct. In one embodiment, the moisture content of the second portion is reduced prior to admixing it with the first portion. The portions can be combined in any suitable ratios, according to the desired properties of the final composition. In another embodiment, the particles of either portion can be coated to further reduce additional di-salt formation or to protect the components from moisture. Other detergent components, such as, for example, fragrances and/or enzymes, can also be added to the admixture as separate portions.
For any of the compositions and methods in accordance with the present invention, the first portion can be formed by, for example, dry-blending, agglomeration and fluid bed mixing. Such methods preferably do not cause more than a minor amount of additional di-salt formation in the first portion. The second portion can be formed by, for example, dry-blending, agglomerating, spray drying, fluid bed mixing, as well as by other methods known to the skilled artisan.